Method for producing a semiconductor component

ABSTRACT

A method for producing a semiconductor component is proposed. The method includes providing a semiconductor body having a first surface; forming a mask on the first surface, wherein the mask has openings for defining respective positions of trenches; producing the trenches in the semiconductor body using the mask, wherein mesa structures remain between adjacent trenches; introducing a first dopant of a first conduction type using the mask into the bottoms of the trenches; carrying out a first thermal step; introducing a second dopant of a second conduction type, which is complementary to the first conduction type, at least into the bottoms of the trenches; and carrying out a second thermal step.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application Serial No.10 2007 029 121.5, which was filed Jun. 25, 2007, and is incorporatedherein by reference in its entirety.

BACKGROUND

Power semiconductor components are optimized in particular with regardto their on-resistance Ron and their breakdown strength. Thus, IGBTs(Insulated Gate Bipolar Transistor) having dynamic adaptability havebeen proposed, for example, which adapt themselves dynamically tovoltage spikes that can occur when the component is switched over to theoff state. The dynamic adaptability of power semiconductor componentsextends their permissible area of use (SOA, safe Operating Area) andmakes it possible to simplify the driving electronics, that is to say todispense with active clamping elements and overvoltage protectiveelements without increasing the total resistance Rt.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments shown in the appended figures are described below, andfurther advantages and modifications will become apparent from saidembodiments. However, the invention is not restricted to thespecifically described embodiments, but rather can be modified andaltered in a suitable manner. It lies within the scope of the inventionto combine individual features and feature combinations from oneembodiment with features and feature combinations from anotherembodiment in a suitable manner in order to attain further embodimentsaccording to the invention.

Embodiments relate generally to semiconductor components. Morespecifically, the embodiments relate to field effect controllablesemiconductor components. They relate especially to power semiconductorcomponents and in particular to field effect semiconductor componentswith or without a bipolar transistor structure. Further embodimentsrelate to a method for producing a semiconductor component which is e.g.controllable by the field effect.

FIGS. 1A to 1F show a first embodiment of a method for producing a fieldeffect controllable semiconductor component.

FIG. 2 shows simulation results for evaluating the breakdown voltageBVces as a function of the implantation dose used.

FIG. 3 shows simulation results for assessing the voltage Vcesat presentacross a semiconductor component in the on state as a function of theimplantation dose used.

FIG. 4 shows simulation results for evaluating the threshold voltageVgeth as a function of the implantation dose used.

FIGS. 5A and 5B show simulation results for illustrating the electricfield strength distribution upon breakdown for a conventionalsemiconductor component (FIG. 5A) and for a semiconductor componentproduced according to the first embodiment (FIG. 5B).

FIGS. 6A and 6B show simulation results for illustrating the impactionization rate for a conventional semiconductor component (FIG. 6A) andfor a semiconductor component produced according to the first embodiment(FIG. 6B).

FIGS. 7A to 7F show individual steps of a production method inaccordance with a second embodiment.

FIG. 8 shows simulation results for the evaluation of the breakdownvoltage BVces as a function of the implantation dose used.

FIG. 9 shows simulation results for assessing the voltage Vcesat presentacross a semiconductor component in the on state as a function of theimplantation dose used.

FIG. 10 shows simulation results for evaluating the threshold voltageVgeth as a function of the implantation dose used.

FIG. 11 shows the implantation conditions for the first embodiment.

FIG. 12 shows the implantation conditions for the second embodiment.

DETAILED DESCRIPTION

Some embodiments will be explained below. In the context of the presentdescription, “laterally” or “lateral direction” is to be understood tomean a direction or extent running parallel to the lateral extent of asemiconductor material or semiconductor body. A semiconductor body istypically present as a thin wafer or chip and has two surfaces situatedon opposite sides, one surface of which is referred to as main surface.The lateral direction thus extends parallel to these surfaces. Incontrast thereto, the term “vertically” or “vertical direction” isunderstood to mean a direction running perpendicular to the main surfaceand thus to the lateral direction. The vertical direction therefore runsin the thickness direction of the wafer or chip.

The embodiments are predominantly described on the basis of field effecttransistors with a bipolar transistor structure, in particular powersemiconductor components and specifically IGBTs with a pnp bipolartransistor structure. However, the embodiments are not restrictedthereto and can also be formed as power field effect transistors, forexample npn field effect transistors. The doping shown in theembodiments can also be correspondingly inverted.

The structures shown in the figures are not depicted as true to scale,but rather serve only to afford a better understanding of theembodiments.

FIGS. 1A to 1F show individual steps of a production method inaccordance with a first embodiment. An aim of this method is to producean n-conducting layer which is buried deep in the semiconductor body andsurrounds trenches and in particular the lower region of the trenchesincluding the trench bottoms. Furthermore, p-doped layers are formedwhich are embedded in the n-doped layer and surround the trench bottoms.What is thereby achieved is that a gate oxide formed at the walls of thetrenches is protected, particularly in the region of the trench bottoms,against high electric field strengths that can occur in the off stateand when the semiconductor component is switched over to the off state.

The starting point of the method is a semiconductor body 2, for example,which typically includes a weakly doped semiconductor region 48. In someexemplary embodiments, the semiconductor region 48 can typically involvethe background doping of the semiconductor body 2, which doping in thepresent embodiment is weakly n-doped (first conduction type) and has adopant concentration of approximately 2*10¹³/cm³. Parts of thissemiconductor region 48 can subsequently form the drift region or thedrift path of the semiconductor component.

An optional deep P-type well 30 can be formed in the semiconductor body2, which well represents the edge region of the semiconductor componentto be formed and surrounds the active region of the semiconductorcomponent. The p-type well 30 can be partly covered with a thermallyoxidized optional field oxide 32.

Irrespective of whether or not the p-type well 30 and the field oxide 32are present, a mask 6 is formed onto a first surface 4 of thesemiconductor body 2. The mask 6 can be a hard mask. In order to formthe mask 6, by way of example, a TEOS layer is deposited over the wholearea and suitably patterned using a resist mask (not shown here),wherein openings 8 that define the position of the later trenches areetched in the TEOS layer as a result. FIG. 1A shows the finishedpatterned mask 6 with the openings 8.

Trenches 10 are formed in the semiconductor body 2 using the mask 6. Forthis purpose, by way of example, the semiconductor material of thesemiconductor body 2 is etched. The etching is effected selectively withrespect to the material of the mask 6 and is typically embodied asanisotropic etching, such that trenches 10 having substantially verticalside walls arise. The trenches 10 are typically etched a few μm deepinto the semiconductor body, wherein the trenches 10 can extend down toa depth of approximately 4 μm to approximately 8 μm.

The type of etching, that is to say the etching gas or gases used andalso the etching time, depends, inter alia, on the material of thesemiconductor body 2 used and the material of the mask 6. In the presentembodiment, the semiconductor body 2 is composed of monocrystallinesilicon, for example. By way of example, the following etching gases aresuitable for the anisotropic etching of silicon: SF₆ and HBr. Instead ofsilicon, however, the semiconductor body 2 can also be composed of othersemiconductor materials, for example silicon carbide (SiC), compoundsemiconductors such as, for example, III-V compound semiconductors andheterostructures of the aforementioned semiconductor materials.

The structure obtained after the etching is shown in FIG. 1A. Thesemiconductor material of the semiconductor body 2 that has remainedbetween adjacent trenches 10 forms mesa structures 12 there, in whichfor example the body regions of the semiconductor component are formedin later method steps.

Afterward, a first dopant is introduced, for example implanted, into thebottoms 14 of the trenches 10 using the mask 6. The mask 6 originallyprovided for the etching of the trenches 10 accordingly also serves asan implantation mask, such that the first dopant 16 in the semiconductorbody 2 is only implanted into the bottoms 14 of the trenches 10. This isindicated in FIG. 1B. The first dopant 16 is, like the background dopingof the semiconductor body 2, of the first conduction type, that is tosay an n-type dopant in the present embodiment. By way of example,phosphorus can be used as the first dopant. The dose can generally liein a range of approximately 1*10¹²/cm² to approximately 3*10¹³/cm². Thedose can also lie in the range of approximately 6*10¹²/cm² toapproximately 3*10¹³/cm². It is likewise possible for the dose even tolie in a range of approximately 8*10¹²/cm² to approximately2.5*10¹³/cm². Arsenic and antimony can also be used instead ofphosphorus. Alternatively, the first dopant 16 can also be introduced bymeans of a furnace process using liquid or solid sources. In the case ofphosphorus, this can be effected for example on the basis of POCl₃.

The mask 6 is subsequently removed for example by means of wet-chemicaletching, for example using buffered HF acid, selectively with respect tothe material of the semiconductor body 2. In this case, the etching canbe effected in a time-controlled manner, that is to say that an etchingwith a predetermined etching time or with end point control is carriedout. A first thermal step, typically a high-temperature thermal step, issubsequently carried out. The implanted first dopant 16 is at leastpartly outdiffused by means of this thermal step. Since the first dopant16 was implanted into the trench bottoms 14, the out diffusion takesplace from this region, that is to say that the out diffusion regionsthat form in the process are formed in the depth of the semiconductorbody 2 and typically at a distance from the first surface 4 of thesemiconductor body 2. If the first thermal step is carried out for aperiod of time such that said out diffusion regions merge with oneanother, this gives rise to a buried and contiguous n-conducting layersurrounding the lower region of the trenches including the bottoms 14.This n-conducting layer, which extends substantially in a lateraldirection, is referred to hereinafter as buffer region 26 or bufferlayer. The buffer region 26 or the out diffusion regions, as indicatedin FIG. 1C, are formed approximately symmetrically with respect to thebottoms 14 in a vertical direction. It goes without saying thatsubsequent thermal steps can lead to a further out diffusion of thefirst dopant 16. This further out diffusion is not represented in thesubsequent figures, for the sake of simplicity. In this case, the extentof the further outdiffusion is greatly dependent on the temperature andthe time duration of the further thermal steps. The out diffusionregions of the first dopant need not necessarily grow together duringthe first thermal step, however. It is also possible for this not totake place until during subsequent thermal steps. However, the firstthermal step is the essential thermal step for forming the separatebuffer regions (if merging is not desired) or the continuous bufferregion 26 (if the out diffusion leads to merging).

The first thermal step can be carried out for example at a temperaturein the range of approximately 1000° C. to approximately 1200° C. and inparticular at approximately 1150° C., for approximately 140 minutes. Thefirst thermal step can also be carried out for longer periods of time.If appropriate, other dopants (not shown here), for example for formingfield rings in the edge region of the semiconductor body 2, can beoutdiffused by means of the first thermal step. In this case, the outdiffusion regions can attain an extent of approximately 3 to 4 μm,measured from the trench bottoms 14. The mesa structures 12 have alateral extent of typically approximately 4 μm to approximately 10 μm.In this case, the dopant concentration of the out diffusion regions orof the buffer region 26 can lie between 4*10¹⁵/cm³ and approximately3*10¹⁶/cm³. It is likewise conceivable for the dopant concentration tolie in a range of approximately 8*10¹⁴/cm³ to approximately 3*10¹⁶/cm³.

As is evident from the comparison of FIGS. 1B and 1C, the first thermalstep also leads to the further out diffusion of the p-well 30. Duringthe first thermal step, an auxiliary oxide layer 20 can furthermore formon the uncovered surfaces of the semiconductor body 2. Said auxiliaryoxide layer 20 covers the first surface 4 and also the uncovered surfaceregions of the trenches 10. The auxiliary oxide layer 20 can serve as ascreen oxide during the subsequent implantation of a second dopant 18.

The implantation of the second dopant 18 (FIG. 1D), which is of thesecond conduction type complementary to the first conduction type, isillustrated in FIG. 1D. The second dopant can be boron, for example. Thedose of the second dopant 18 can lie in a range of approximately3*10¹²/cm² to approximately 1*10¹⁴/cm². It is likewise possible to workwith a dose of approximately 4*10¹³/cm² to approximately 1*10¹⁴/cm².Furthermore, the dose can lie in a range of approximately 6*10¹³/cm² to9*10¹³/cm², for example can be approximately 8*10¹³/cm². In this case,the implantation is effected both into the trench bottoms 14 and intothe uncovered regions of the first surface 4, that is to say inparticular into the regions of the mesa structures 12 that are near thesurface.

After the second dopant 18 has been implanted, the auxiliary oxide layer20 is removed wet-chemically, for example. A gate oxide layer 22 canthen be formed in particular thermally, wherein the gate oxide layerlines the trenches 10 in particular, and can also cover the uncoveredregions of the semiconductor material of the semiconductor body 2 at thefirst surface 4 thereof.

The trenches 10 are subsequently filled with a conductive material, forexample polysilicon. This can be done for example by deposition of apolysilicon layer with subsequent doping and patterning thereof. Thepolysilicon layer is typically highly doped, such that the polysiliconin the trenches 10 can have a dopant concentration of approximately1*10²⁰/cm³. The conductive material filled into the trenches 10 formsthere the gate electrode 24 for the individual cells of thesemiconductor component. The gate electrodes 24 arranged in the trenches10 are accordingly insulated from the semiconductor body 2 by a gatedielectric 22.

Afterward, a second thermal step is effected for the at least partial orlargely complete out diffusion of the implanted second dopant 18. Thesecond thermal step can be carried out at a temperature in the range ofapproximately 1000° C. to approximately 1200° C., and in particular atapproximately 1150° C., for approximately 60 minutes. The first thermalstep is typically effected at substantially the same temperature as thesecond thermal step, but for a longer time. As already described furtherabove, the second thermal step can likewise lead to a further outdiffusion of the first dopant 16. By means of the second thermal step,the second dopant 18 implanted into the trench bottoms 14 is at leastpartly outdiffused with formation of buried protective regions 28 thatare typically completely embedded into the buffer region 26. In thiscase, the protective regions 28 largely completely surround the trenchbottoms 14 and are formed approximately symmetrically with respect tothe trench bottoms 14 in a vertical direction. The protective regions 28are typically completely surrounded by the buffer region 26. Theprotective regions 28 can have a dopant concentration of approximately2*10¹⁵/cm³ to approximately 1*10¹⁷/cm³, and in some variants ofapproximately 3*10¹⁶/cm³ to approximately 1*10¹⁷/cm³. The second thermalstep is the essential thermal step with regard to the out diffusion ofthe second dopant 18.

The second dopant 18 implanted into the regions of the mesa structures12 that are near the surface is furthermore outdiffused into thesemiconductor body 2 by means of the second thermal step. Body regions34 are formed between the trenches 10 as a result. The body regions 34can have a maximum dopant concentration of approximately 5*10¹⁶/cm³ toapproximately 5*10¹⁷/cm³. As shown in FIG. 1E, the body regions 34directly adjoin the buffer region 26 and lead to the formation of a pnjunction 35 there. In principle the body regions 34 can respectivelyform a pn junction with the buffer region 26 and/or the semiconductorregion or drift region 48. The vertical position of the substantiallylaterally extending pn junction 35 depends on the depth of the trenches10, the implantation dose used for the first and second dopants, andalso the temperature and length of the first and second thermal steps.The diffusion constant of the individual dopants likewise plays a part.

As is evident from FIGS. 1C and 1E, the buffer region 26 and the bodyregions 34 diffuse toward one another since the out diffusion of thebody regions 34 takes place from the regions of the mesa structures 12that are near the surface and the out diffusion of the buffer region 26takes place from the region of the trench bottoms 14. The out diffusionof the buffer region 26 from the depth of the semiconductor body 2, thatis to say from the region of the trench bottoms 14, improves theproperties of the semiconductor component.

Firstly, the out diffusion of the buffer region begins precisely inthose regions in the semiconductor body 2 in which the buffer region 26is intended to be formed. This represents an improvement in particularin comparison with those production methods in which an out diffusiontakes place from the surface of the semiconductor body. This is becausein such production methods, the introduced dopant for forming a bufferregion has to be outdiffused for a very long time or at very hightemperatures in order that the buffer region 26 also encloses thebottoms of the trenches 10. Therefore, the method of the presentembodiment can significantly reduce the diffusion time or diffusiontemperature and hence the required thermal budget. Moreover, theformation of the buffer region 26 takes place practically automaticallyaround the trench bottoms 14.

Secondly, since the first dopant is implanted only into the trenchbottoms 14 and not into regions of the mesa structures 12 that are nearthe surface, the first dopant 16 also does not act as background dopingfor the second dopant 18 in the mesa structures 12. As a result, theimplantation dose for the second dopant 18 can be comparatively low,whereby the properties of the body regions 34 can be established in atargeted manner more easily in particular with regard to a low channeldoping and increased channel mobility of the charge carriers. Theintended implantation of the first dopant 16 only into the trenchbottoms 14 likewise has a favorable effect on the threshold voltage ofthe semiconductor components. Since the first dopant 16 is not implantedinto the mesa structures 12, nor can it influence the threshold voltageof the semiconductor components there. Local fluctuations of theimplanted dose are often observed during implantation methods, whichfluctuations can lead to fluctuations of the dopant concentration andtherefore also of the threshold voltage. By avoiding the implantation ofthe first dopant 16 into the mesa structures 12, therefore, it ispossible to significantly reduce the fluctuations of the thresholdvoltage between adjacent cells.

Another factor contributing to the improvement is that no additionalimplantation masks are used, rather only the mask 6 used for the etchingof the trenches 10 is subsequently also used as an implantation mask. Asa result, the production method is cost-effective overall.

Consequently, the production method requires no additional masks, leadsneither to an increase in the thermal budget nor to an increase in theprocess steps required, and at the same time prevents a highconcentration of the second dopant 18 in the channel region that canlead to undesirable variations of the threshold voltage of theindividual cells of the semiconductor component.

It is favorable to set a ratio of the implantation dose of first dopantto second dopant 18 of approximately 1:3 to approximately 1:10. What isthereby achieved is that the ratio of the dopant concentration of bufferregion 26 to protective regions 28 in the region of the trench bottoms14 lies approximately between 1:4 and approximately 1:12. These rangeshave proved to be favorable for the performance of semiconductorcomponents and in particular for avoiding electrical breakdowns in theregion of the trench bottoms 14.

To afford a better understanding of the suitable implantation doses forthe first embodiment, reference is made to FIG. 11, which shows agraphical representation of suitable implantation doses. 60 indicatesthe maximum range for the phosphorus implantation dose (approximately6*10¹²/cm² to approximately 3*10¹³/cm²) and the boron implantation dose(approximately 4*10¹³/cm² to approximately 1*10¹⁴/cm²) for one example,while 61 indicates the range for a second example (phosphorus:approximately 8*10¹²/cm² to approximately 2.5*10¹³/cm²; boron:approximately 6*10¹³/cm² to approximately 9*10¹³/cm²). In this case, itis also possible additionally to take account of the secondary conditionwith regard to the ratio of the implantation doses of phosphorus toboron, wherein 62 shows one limit of the ratio of 1:10 and 63 shows theother limit of the ratio of 1:3. By way of example, the implantationdoses can be chosen such that they lie within the range 60 and inaddition within the range between the straight lines 62 and 63. On theother hand, the implantation doses can also lie within the range 61 andthe straight lines 62 and 63. It has been shown in some examples thatthe boron implantation dose (second dopant) should be chosen to be ashigh as possible in relation to the phosphorus implantation dose (forexample 8*10¹³/cm²), in order to be able to set the threshold voltageVgeth in a suitable manner.

Finally, a semiconductor region 50 of the second conduction type, forexample an emitter region 50, can be formed at a second surface56—opposite the first surface 4—of the semiconductor body 2 by means of,for example, suitable implantation or coating and outdiffusion. A fieldstop layer (not shown here) which is a highly doped n-conducting layer,can also be formed between the semiconductor region or emitter region 50and the drift region 48. A rear side electrode 52 with an electrodeconnection 54 can then be formed on the second surface 56.

Source regions 36 of the first conduction type and body contact regions38 of the second conduction type can be formed in regions of the mesastructures 12 that are near the surface. The source regions 36 aretypically produced in the body regions 34. The source regions 36 can beproduced in such a way that they are arranged in the mesa structures 12at the first surface 4 and adjoin the trenches 10. The source regions 36are highly doped n-conducting regions and can have a maximum dopantconcentration of approximately 1*10²⁰/cm³ to approximately 1*10²¹/cm³.The source regions 36 form a pn junction 37 with the body regions 34 andadjoin the trenches 10. The body contact regions 38 are highly dopedp-conducting regions and can have a dopant concentration ofapproximately 1*10¹⁸/cm³ to approximately 1*10²⁰/cm³. The trenches 10are closed off with an insulation region 40, such that they areinsulated from the front side electrode 44 that is subsequently to beapplied. Contact is made with the gate electrodes 24 arranged in thetrenches 10 by means of suitable gate connections 42. The front sideelectrode 44 is connected to an electrode connection 46. The structurethus obtained is illustrated in FIG. 1F. Here this is an IGBT. As analternative it is possible to produce a power field effect transistor.In this case, instead of the emitter region 50 shown in FIG. 1F, ann-doped drain region having a higher dopant concentration than the driftregion 48 is produced at the second surface 56 of the semiconductor body2. So-called vertical components are involved in both cases since thecurrent flow essentially runs from the first surface 4 to the secondsurface 56.

The individual trenches 10 define separate cells of a semiconductorcomponent which together form a power semiconductor component. Theeffective cross section for the current flow can be correspondinglyincreased by forming correspondingly many cells such that powersemiconductor components having high rated currents typically have manycells. In this case, the cell shown in the right-hand region in FIG. 1Fforms an edge cell. Toward the left, the structure continuessymmetrically and is then once again terminated by an edge cell.

The trenches 10 are typically formed at a distance from the drift region48 and above the latter. In the present embodiment, the buffer region 26completely surrounds the lower region of the trenches 10, such that thetrenches 10 are arranged above the drift region 48. The buffer region 26likewise adjoins the body regions 34. If the buffer region 26 is notformed as a continuous layer, the drift region 48 can also reach betweenthe trenches 10 as far as the body regions 34. However, the lower regionof the trenches 10 including the trench bottoms 14 typically remainscompletely surrounded by the buffer region 26 and the protective regions28. It is likewise possible for the buffer region 26 to be formed as acontinuous layer without being in direct contact with the body regions34. In this case, the buffer region 26 is formed as a buried layer inthe drift region 48 and the pn junction forms between a region of thedrift region 48 that remains above the buffer region 26 and the bodyregions 34. The body regions 34 are typically arranged above the trenchbottoms 14 and at a distance from the latter.

The method of operation of the buffer region 26 and of the protectiveregions 28 will be explained, without wishing to be restrictive, on thebasis of the structure of an IGBT as shown in FIG. 1F. In the off-statecase, the reverse voltage is reduced in the buffer region 26 or thedrift region 48. If the electrical conditions are imagined on the basisof the potential lines, then high field strengths occur in those regionsin which the potential lines are closely packed. In this case, theposition of the potential lines is determined by the dopant distributionand geometrical boundary conditions. In homogeneities typically lead toa compaction of the potential lines and thus to a local increase in thefield strength. Therefore, high field strengths are also observed in theregion of the trench bottoms 14. The p-doped protective regions 28 nowalter the electrical conditions in such a way that the electricalpotential lines are at least partly forced out from the direct vicinityaround the trench bottoms 14. As a result, the formation of high fieldstrengths is avoided there. This is illustrated for example in FIGS. 5Aand 5B. In this case, FIG. 5A shows the structure of a conventionalsemiconductor component which does not contain a protective region ofthe second conduction type in the region of the trench bottoms 14. Ascan be discerned, the electric field strength is comparatively highthere directly below the trench bottom. In contrast thereto, as shown inFIG. 5B, the maximum of the electric field strength is shifted furtherinto the depth of the semiconductor body 2 and from the region of thetrench bottoms 14. This is achieved by means of the protective regions28.

This is also associated with a shift in the location of the highestimpact ionization rate during breakdown, as can be discerned from thecomparison of FIGS. 6A and 6B. On account of the protective regions 28,the maximum of the impact ionization rate is locally displaced from thetrenches 10, and in particular the trench bottoms, whereby theprobability that hot charge carriers can be injected into the gate oxide22 is significantly reduced. The injection of hot charge carriers intothe gate oxide 22 is responsible for a shift in the switching parametersduring reliability tests in which currents that are 2 to 7 times as highas the rated current of the semiconductor component are multiplyswitched. Hot charge carriers possibly injected in this case would leadin the long term to the failure of the semiconductor component.Therefore, the protective regions 28 improve the long-term reliabilityof the semiconductor components.

As has been found in experiments, the shift in the breakdown locationaway from the gate oxide also leads to improved dynamic switchingproperties of the semiconductor component, which is thus better able toadapt itself dynamically to voltage spikes that can occur for example asa result of self-induction when high load currents are switched off.

Furthermore, the more highly doped buffer region 26 in comparison withthe drift region 48 leads to an improvement in the component propertiesin the on-state case, since the more highly doped buffer region 26 leadsto a reduction of the on resistance Ron.

FIGS. 2 to 4 reveal the influence of the boron implantation dose, thatis to say the implantation dose of the second dopant 18, on thebreakdown voltage BVces (FIG. 2), the voltage Vcesat in the switched-onstate (FIG. 3), and the threshold voltage Vgeth (FIG. 4). BVces denotesthe voltage between front electrode 44, which in terms of circuitry isalso referred to as emitter, and the rear side electrode 52, which interms of circuitry is also referred to as collector. Vcesat is likewisedetermined between front electrode 44 and rear side electrode 50. Vgethis the voltage which has to be applied to the gate electrode 24 in orderthat a conductive channel is established in the body region 34.

The corresponding dependencies were plotted for various phosphorusimplantation doses, i.e. dose of the first dopant 16. The respectivephosphorus implantation doses in cm⁻² are indicated in the correspondinglegend for each curve. It can be discerned that the boron implantationdose, i.e. the second implantation, should be higher than the phosphorusimplantation dose. Favorable process parameters for the embodiment shownin FIGS. 1A to 1F are for example a phosphorus implantation dose of1*10¹³/cm² and a boron implantation dose of approximately 8*10¹³/cm².This results in a ratio of the implantation doses of approximately 1:8.The implantation doses chosen lead to a dopant concentration of thebuffer region 26 of approximately 8*10¹⁵/cm³ and of the protectiveregions 28 of approximately 8*10¹⁶/cm³. This corresponds to a ratio ofthe dopant concentrations of approximately 1:10. The slightly increasedratio of the dopant concentrations in comparison with the implantationdoses is caused by the fact that the buffer region 26 outdiffusesspatially further than the protective regions 28. The formation ofbuffer region 26 or buffer regions 26 and protective regions 28 alsoleads to the improvement of the coordination between Vcesat-Eoff(Vcesat-Eoff trade-off).

A second embodiment of the production method is described with referenceto FIGS. 7A to 7F. The first steps of this embodiment, which are shownin FIGS. 7A and 7B, correspond to the steps shown in FIGS. 1A and 1B. Arepetition of the description is therefore dispensed with.

In contrast to the first embodiment, after the implantation of the firstdopant 16 has taken place, the mask 6 is not removed. Therefore, themask 6 also remains on the first surface of the semiconductor body 2during the first thermal step. As a result, during the outdiffusion ofthe first dopant 16, auxiliary oxide layers 20 arise only on theuncovered surface regions of the trenches 10. The first thermaltreatment of the second embodiment can be carried out, in principle,with the same process parameters as in the first embodiment. The firstdopant can also be implanted with a dose of approximately 2*10¹²/cm² toapproximately 2*10¹³/cm². The structure thus obtained is shown in FIG.7C.

The second dopant 18 is subsequently implanted using the mask 6. Onaccount of the mask 6, the implantation is effected only into the trenchbottoms 14. In principle, it is possible to work with the same dose asin the first embodiment. In comparison with the first embodiment, theimplantation dose of the second dopant 18, which is boron here, can alsobe changed and in particular reduced. By way of example, it is possibleto work in a range of approximately 1.2*10¹³/cm² to approximately6*10¹³/cm². It is likewise possible to set the dose to values of betweenapproximately 2*10¹³/cm² and approximately 5*10¹³/cm². As a result, theratio of the implantation dose of first dopant 16 to second dopant 18lies for example approximately between 1:3 and approximately 1:5.

Typical implantation doses for the second embodiment can be gatheredfrom FIG. 12, wherein 70 shows a range for the phosphorus implantationdose of approximately 1*10¹²/cm² to approximately 3*10¹³/cm² and theboron implantation dose of approximately 3*10¹²/cm² to approximately1*10¹⁴/cm² for a first example. 71 indicates a range for a secondexample (phosphorus: from approximately 2*10¹²/cm² to approximately2*10¹³/cm²; boron: approximately from 1.2*10¹³/cm² to approximately6*10¹³/cm²). Secondary conditions with regard to the ratio of theimplantation doses of phosphorus to boron can additionally be taken intoaccount, wherein 72 indicates a ratio of 1:10 and 73 a ratio of 1:3. Theimplantation doses can be chosen such that they lie within the regions70 and 71 and additionally within the straight lines 72 and 73. Theimplantation doses can be reduced in comparison with the firstembodiment.

By means of a subsequent second thermal treatment, the second dopant 18is outdiffused and in the process forms protective regions 28 in theregion of the trench bottoms 14. The auxiliary oxide layers 20 and alsothe mask 6 are then removed in a suitable manner, for examplewet-chemically.

The implantation dose of the second dopant 18 can be scaled in asuitable manner depending on the implantation dose of the first dopant.By way of example, it is possible to implant the second dopant 18 withan implantation dose that is approximately 4 times as high as that ofthe first dopant 16. This ensures that the second dopant 18 is alwayspresent in a sufficiently high concentration. However, it is alsopossible to reduce the implantation dose of the second dopant to valuesof approximately 1.5*10¹³/cm² to approximately 2*10¹³/cm². In this case,however, the implantation dose of the first dopant should be chosen tobe correspondingly low in order to avoid a fall in the breakdown voltageBVces, as can be seen for example from FIG. 8.

Afterward, in a manner comparable with the steps described in connectionwith FIG. 1E of the first embodiment, the gate electrodes 24 are formedin the trenches 10, that is to say that the trenches 10 are largelyfilled with a conductive material 24. A third dopant 19 is thenintroduced, for example implanted, into regions of the mesa structures12 that are near the surface. The third dopant 19 can be boron, forexample, which is implanted with an implantation dose of approximately8*10¹²/cm² to approximately 5*10¹³/cm². As a result of the trenches 10being filled with the conductive material, the trench bottoms 14 areprotected, such that during the implantation of the third dopant 19, thelatter is not implanted into the trench bottoms 14. The structure thusobtained is shown in FIG. 7E.

The outdiffusion of the third dopant 19 is effected by means of asubsequent third thermal step, whereby the body regions 34 are formed inthe mesa structures 12. If appropriate, the second thermal step can alsobe combined with the third thermal step, such that body regions andprotective regions are then outdiffused simultaneously. The structurethus obtained is shown in FIG. 7F. The third thermal step can be carriedout at a temperature in the range of approximately 1100° C. toapproximately 1200° C., and in particular at approximately 1150° C., forapproximately 60 minutes.

In this embodiment, the implantation for the formation of the protectiveregions 28 and of the body regions 34 take place independently of oneanother and can thereby be better adapted to the desired requirements.Moreover, the separate thermal steps permit better control of theoutdiffusion. By way of example, the implantation dose for the firstdopant 16 can be in the region of approximately 1*10¹³/cm² and theimplantation dose for the second dopant 18 can be approximately4*10¹³/cm². This corresponds to a ratio of the implantation doses ofapproximately 1:4. These implantation doses lead to a dopantconcentration of the buffer region 26 of approximately 8*10¹⁵/cm³ and ofthe protective regions 28 of approximately 4*10¹⁶/cm³. This correspondsto a ratio of approximately 1:5. The dopant concentration of the seconddopant 18 can therefore be reduced in comparison with the firstembodiment. However, this does not have a disadvantageous effect on thedopant concentration of the body regions 34 since a separateimplantation is effected for producing said body regions. In principle,the dopant concentration for the buffer region 26 can lie betweenapproximately 8*10¹⁴/cm³ and approximately 3*10¹⁶/cm³ and the dopantconcentration for the protective regions 28 can lay betweenapproximately 2*10¹⁵/cm³ and approximately 1*10¹⁷/cm³.

Finally, in a manner comparable with the steps described in connectionwith FIG. 1F of the first embodiment, an emitter region or a drainregion, the rear side electrode and also the source regions, bodycontact regions and the front side electrode are formed.

As in the first embodiment, the method of the second embodiment requiresno further masks. In this case, too, the outdiffusion takes place “fromthe depth” of the semiconductor body 2. The method of the secondembodiment likewise permits the same or comparable structures havingcomparable properties with respect to the method in accordance with thefirst embodiment to be produced, for which reason a repetition isdispensed with.

FIGS. 8 to 10 show simulation results with regard to the breakdownvoltage BVces (FIG. 8), the voltage Vcesat in the switched-on state(FIG. 9) and the threshold voltage Vgeth (FIG. 10) as a function of thephosphorus and boron implantation dose. The simulation results shownhere are based on semiconductor components that were produced inaccordance with the second embodiment. The boron implantation dosesindicated relate to the implantation of the second dopant 18 into thetrench bottoms 14. A trench depth of approximately 4 μm was taken as abasis for all the simulations. The respective boron implantation dose isindicated directly in the curves in which the boron implantation dosescales with the phosphorus implantation dose. In the other curves, therespective constant boron implantation dose is indicated in the legend.The implantation doses are indicated in cm⁻².

As can be discerned, for comparatively low phosphorus implantation dosesof less than 1*10¹³/cm², the breakdown voltage BVces is very high. Thefall in the breakdown voltage BVces above a phosphorus implantation doseof approximately 1*10¹³/cm² can be compensated for by increasing theboron implantation dose or by scaling the boron implantation dose withthe phosphorus implantation dose, for example in the ratio of 1:4 ofphosphorus implantation dose to boron implantation dose. In simulationsand experiments that are not shown here, it has likewise been found thatthe breakdown voltage Bvces is lower in the case of identicalimplantation doses but with a trench depth of approximately 6 μm. Sincethe implantation doses can be varied in a comparatively large range inthe second embodiment, Bvces, Vcesat and Vgeth can be set in a suitablemanner even with variation of the trench depth.

The invention is not restricted to the embodiments described above, butrather encompasses suitable modifications within the scope manifested bythe claims. The appended claims should be understood as a first,non-binding attempt to describe the invention using general words.

1. A method for producing a semiconductor component, comprising:providing a semiconductor body comprising a first surface; forming amask on the first surface, wherein the mask comprises openings fordefining respective positions of trenches; producing the trenches in thesemiconductor body using the mask, wherein mesa structures remainbetween adjacent trenches; introducing a first dopant of a firstconduction type using the mask into the bottoms of the trenches;carrying out a first thermal step, wherein the first dopant is at leastpartly outdiffused in order to form at least one buried buffer region;introducing a second dopant of a second conduction type, which iscomplementary to the first conduction type, at least into the bottoms ofthe trenches; and carrying out a second thermal step, wherein the maskis removed before the second dopant is introduced, such that when thesecond dopant is introduced, the second dopant is also introduced intothe mesa structures, and wherein, by means of the second thermal step,the second dopant introduced into the mesa structures is at least partlyoutdiffused in order to form body regions in the mesa structures.
 2. Themethod as claimed in claim 1, wherein the first and the second dopantare in each case introduced by means of implantation into thesemiconductor body.
 3. The method as claimed in claim 2, wherein theratio of the implantation dose of first dopant to second dopant liesbetween approximately 1:3 and approximately 1:10.
 4. The method asclaimed in claim 2, wherein the first dopant is implanted with a dose ofapproximately 1*10¹²/cm² to approximately 3*10¹³/cm².
 5. The method asclaimed in claim 2, wherein the second dopant is implanted with a doseof approximately 3*10¹²/cm² to approximately 1*10¹⁴/cm².
 6. The methodas claimed in claim 1, wherein, by means of the second thermal step, thesecond dopant is at least partly outdiffused in order to form protectiveregions.
 7. The method as claimed in claim 1, wherein the first dopantis implanted with a dose of approximately 6*10¹²/cm² to approximately3*10¹³/cm².
 8. The method as claimed in claim 1, wherein the seconddopant is implanted with a dose of approximately 4*10¹³/cm² toapproximately 1*10¹⁴/cm².
 9. The method as claimed in claim 1, whereinthe second dopant is introduced using the mask.
 10. The method asclaimed in claim 9, wherein the first dopant is implanted with a dose ofapproximately 2*10¹²/cm² to approximately 2*10¹³/cm².
 11. The method asclaimed in claim 9, wherein the second dopant is implanted with a doseof approximately 1.2*10¹³/cm² to approximately 6*10¹³/cm².
 12. Themethod as claimed in claim 1, wherein at least two adjacent buriedbuffer regions are merged.
 13. A method for producing a semiconductorcomponent, comprising: providing a semiconductor body comprising a firstsurface; forming a mask on the first surface, wherein the mask comprisesopenings for defining respective positions of trenches; producing thetrenches in the semiconductor body using the mask, wherein mesastructures remain between adjacent trenches; introducing a first dopantof a first conduction type using the mask into the bottoms of thetrenches; carrying out a first thermal step; introducing a second dopantof a second conduction type, which is complementary to the firstconduction type, at least into the bottoms of the trenches using themask; carrying out a second thermal step; removing the mask afterintroducing the second dopant; introducing a third dopant of the secondconduction type into the mesa structures; and carrying out a thermalstep in which the third dopant is at least partly outdiffused in orderto form body regions.
 14. The method as claimed in claim 13, wherein thethird dopant is implanted into the mesa structures.
 15. The method asclaimed in claim 14, wherein the third dopant is implanted with a doseof approximately 8*10¹²/cm² to approximately 5*10¹³/cm².
 16. A methodfor producing a semiconductor component, comprising: providing asemiconductor body comprising a first surface; foaming a mask on thefirst surface, wherein the mask comprises openings for definingrespective positions of trenches; producing the trenches in thesemiconductor body using the mask, wherein mesa structures remainbetween adjacent trenches; introducing a first dopant of a firstconduction type using the mask into the bottoms of the trenches;carrying out a first thermal step; introducing a second dopant of asecond conduction type, which is complementary to the first conductiontype, at least into the bottoms of the trenches; and carrying out asecond thermal step, wherein the second dopant is at least partlyoutdiffused in order to form protective regions, wherein the mask isremoved before the second dopant is introduced, such that when thesecond dopant is introduced, the second dopant is also introduced intothe mesa structures, and wherein, by means of the second thermal step,the second dopant introduced into the mesa structures is at least partlyoutdiffused in order to form body regions in the mesa structures.